Andes

The Andes mountain range, as seen from an airplane, between Santiago de Chile and Mendoza, Argentina, in summer. The large ice field corresponds to the southern slope of San José volcano (left) and Marmolejo (right). Tupungato at their right.

The Andes Mountains are the highest mountain range outside Asia. The highest mountain outside Asia, Argentina's Mount Aconcagua, rises to an elevation of about 6,961 m (22,838 ft) above sea level. The peak of Chimborazo in the Ecuadorian Andes is farther from the Earth's center than any other location on the Earth's surface, due to the equatorial bulge resulting from the Earth's rotation. The world's highest volcanoes are in the Andes, including Ojos del Salado on the Chile-Argentina border, which rises to 6,893 m (22,615 ft).

The Andes are also part of the American Cordillera, a chain of mountain ranges (cordillera) that consists of an almost continuous sequence of mountain ranges that form the western "backbone" of North America, Central America, South America and Antarctica.

Etymology

The etymology of the word Andes has been debated. The majority consensus is that it derives from the Quechua word anti, which means "east"[1] as in Antisuyu (Quechua for "east region"),[1] one of the four regions of the Inca Empire.

The term cordillera comes from the Spanish word cordel, meaning "rope",[2] and is used as a descriptive name for several contiguous sections of the Andes, as well as the entire Andean range, and the combined mountain chain along the western part of the North and South American continents.

Geography

Aerial view of Valle Carbajal in the Fuegian The Andes range is about 200 km (124 mi) wide throughout its length, except in the Bolivian flexure where it is about 640 kilometres (398 mi) wide.

in Venezuela, Colombia, and Ecuador. In the northern part of the Andes, the separate Sierra Nevada de Santa Marta range is often treated as part of the Northern Andes.[3]

The Leeward Antilles islands Aruba, Bonaire, and Curaçao, which lie in the Caribbean Sea off the coast of Venezuela, were formerly thought to represent the submerged peaks of the extreme northern edge of the Andes range, but ongoing geological studies indicate that such a simplification does not do justice to the complex tectonic boundary between the South American and Caribbean plates.[4]

The Andean orogen has a series of bends or oroclines. The Bolivian Orocline is a seaward concave bending in the coast of South America and the Andes Mountains at about 18° S.[5][6] At this point, the orientation of the Andes turns from Northwest in Peru to South in Chile and Argentina.[6] The Andean segment north and south of the Orocline have been rotated 15° to 20° counter clockwise and clockwise respectively.[6][7] The Bolivian Orocline area overlaps with the area of maximum width of the Altiplano Plateau and according to Isacks (1988) the Orocline is related to crustal shortening.[5] The specific point at 18° S where the coastline bends is known as the "Arica Elbow".[8] Further south lies the Maipo Orocline a more subtle Orocline between 30° S and 38°S with a seaward-concave break in trend at 33° S.[9] Near the southern tip of the Andes lies the Patagonian Orocline.[10]

The formation of the modern Andes began with the events of the Triassic when Pangaea began the break up that resulted in developing several rifts. The development continued through the Jurassic Period. It was during the Cretaceous Period that the Andes began to take their present form, by the uplifting, faulting and folding of sedimentary and metamorphic rocks of the ancient cratons to the east. The rise of the Andes has not been constant, as different regions have had different degrees of tectonic stress, uplift, and erosion.

Volcanism

This photo from the ISS shows the high plains of the Andes Mountains in the foreground, with a line of young volcanoes facing the much lower Atacama Desert

The Andes range has many active volcanoes distributed in four volcanic zones separated by areas of inactivity. The Andean volcanism is a result of subduction of the Nazca Plate and Antarctic Plate underneath the South American Plate. The belt is subdivided into four main volcanic zones that are separated from each other by volcanic gaps. The volcanoes of the belt are diverse in terms of activity style, products and morphology. While some differences can be explained by which volcanic zone a volcano belongs to, there are significant differences inside volcanic zones and even between neighbouring volcanoes. Despite being a type location for calc-alkalic and subduction volcanism, the Andean Volcanic Belt has a large range of volcano-tectonic settings, such as rift systems and extensional zones, transpressional faults, subduction of mid-ocean ridges and seamount chains apart from a large range of crustal thicknesses and magma ascent paths, and different amount of crustal assimilations.

Ore deposits and evaporates

The Andes Mountains host large ore and salt deposits and some of their eastern fold and thrust belt acts as traps for commercially exploitable amounts of hydrocarbons. In the forelands of the Atacama Desert some of the largest porphyry copper mineralizations occurs making Chile and Peru the first and second largest exporters of copper in the world. Porphyry copper in the western slopes of the Andes has been generated by hydrothermal fluids (mostly water) during the cooling of plutons or volcanic systems. The porphyry mineralization further benefited from the dry climate that let them largely out of the disturbing actions of meteoric water. The dry climate in the central western Andes has also led to the creation of extensive saltpeter deposits which were extensively mined until the invention of synthetic nitrates. Yet another result of the dry climate are the salars of Atacama and Uyuni, the first one being the largest source of lithium today and the second the world's largest reserve of the element. Early Mesozoic and Neogene plutonism in Bolivia's Cordillera Central created the Bolivian tin belt as well as the famous, now depleted, deposits of Cerro Rico de Potos��.

Climate and hydrology

The climate in the Andes varies greatly depending on latitude, altitude, and proximity to the sea. Temperature, atmospheric pressure and humidity decrease in higher elevations. The southern section is rainy and cool, the central section is dry. The northern Andes are typically rainy and warm, with an average temperature of 18 °C (64 °F) in Colombia. The climate is known to change drastically in rather short distances. Rainforests exist just kilometres away from the snow-covered peak Cotopaxi. The mountains have a large effect on the temperatures of nearby areas. The snow line depends on the location. It is at between 4,500 and 4,800 m (14,800 and 15,700 ft) in the tropical Ecuadorian, Colombian, Venezuelan, and northern Peruvian Andes, rising to 4,800–5,200 m (15,700–17,100 ft) in the drier mountains of southern Peru south to northern Chile south to about 30°S before descending to 4,500 m (14,760 ft) on Aconcagua at 32°S, 2,000 m (6,600 ft) at 40°S, 500 m (1,640 ft) at 50°S, and only 300 m (980 ft) in Tierra del Fuego at 55°S; from 50°S, several of the larger glaciers descend to sea level.[15]

The Andes of Chile and Argentina can be divided in two climatic and glaciological zones: the Dry Andes and the Wet Andes. Since the Dry Andes extend from the latitudes of Atacama Desert to the area of Maule River, precipitation is more sporadic and there are strong temperature oscillations. The line of equilibrium may shift drastically over short periods of time, leaving a whole glacier in the ablation area or in the accumulation area.

Though precipitation increases with the height, there are semiarid conditions in the nearly 7,000-metre (23,000 ft) highest mountains of the Andes. This dry steppe climate is considered to be typical of the subtropical position at 32–34° S. The valley bottoms have no woods, just dwarf scrub. The largest glaciers, as e.g. the Plomo glacier and the Horcones glaciers, do not even reach 10 km (6.2 mi) in length and have an only insignificant ice thickness. At glacial times, however, c. 20,000 years ago, the glaciers were over ten times longer. On the east side of this section of the Mendozina Andes, they flowed down to 2,060 m (6,760 ft) and on the west side to about 1,220 m (4,000 ft) above sea level.[17][18] The massifs of Cerro Aconcagua (6,961 m (22,838 ft)), Cerro Tupungato (6,550 m (21,490 ft)) and Nevado Juncal (6,110 m (20,050 ft)) are tens of kilometres away from each other and were connected by a joint ice stream network. The Andes' dendritic glacier arms, i.e. components of valley glaciers, were up to 112.5 km (69.9 mi) long, over 1,250 m (4,100 ft) thick and overspanned a vertical distance of 5,150 m (16,900 ft). The climatic glacier snowline (ELA) was lowered from 4,600 m (15,100 ft) to 3,200 m (10,500 ft) at glacial times.[17][19][20][21][22][23][24][25][26]

Flora

The Andean region cuts across several natural and floristic regions due to its extension from Caribbean Venezuela to cold, windy and wet Cape Horn passing through the hyperarid Atacama Desert. Rainforests and tropical dry forests[27] used to encircle much of the northern Andes but are now greatly diminished, especially in the Chocó and inter-Andean valleys of Colombia. Opposite of the humid Andean slopes are the relatively dry Andean slopes in most of western Peru, Chile and Argentina. Along with several Interandean Valles, they are typically dominated by deciduous woodland, shrub and xeric vegetation, reaching the extreme in the slopes near the virtually lifeless Atacama Desert.

About 30,000 species of vascular plants live in the Andes, with roughly half being endemic to the region, surpassing the diversity of any other hotspot.[28] The small tree Cinchona pubescens, a source of quinine which is used to treat malaria, is found widely in the Andes as far south as Bolivia. Other important crops that originated from the Andes are tobacco and potatoes. The high-altitude Polylepis forests and woodlands are found in the Andean areas of Colombia, Ecuador, Peru, Bolivia and Chile. These trees, by locals referred to as Queñua, Yagual and other names, can be found at altitudes of 4,500 m (14,760 ft) above sea level. It remains unclear if the patchy distribution of these forests and woodlands is natural, or the result of clearing which began during the Incan period. Regardless, in modern times the clearance has accelerated, and the trees are now considered to be highly endangered, with some believing that as little as 10% of the original woodland remains.[29]

Fauna

The Andes are rich in fauna: With almost 1,000 species, of which roughly 2/3 are endemic to the region, the Andes are the most important region in the world for amphibians.[28]
The diversity of animals in the Andes is high, with almost 600 species of mammals (13% endemic), more than 1,700 species of birds (about 1/3 endemic), more than 600 species of reptile (about 45% endemic), and almost 400 species of fish (about 1/3 endemic).[28]

The Andes Mountains form a north–south axis of cultural influences. A long series of cultural development culminated in the expansion of the Inca civilization and Inca Empire in the central Andes during the 15th century. The Incas formed this civilization through imperialisticmilitarism as well as careful and meticulous governmental management.[34] The government sponsored the construction of aqueducts and roads in addition to preexisting installations. Some of these constructions are still in existence today.

Devastated by European diseases to which they had no immunity and civil wars, in 1532 the Incas were defeated by an alliance composed of tens of thousands of allies from nations they had subjugated (e.g. Huancas, Chachapoyas, Cañaris) and a small army of 180 Spaniards led by Francisco Pizarro. One of the few Inca sites the Spanish never found in their conquest was Machu Picchu, which lay hidden on a peak on the eastern edge of the Andes where they descend to the Amazon. The main surviving languages of the Andean peoples are those of the Quechua and Aymara language families. Woodbine Parish and Joseph Barclay Pentland surveyed a large part of the Bolivian Andes from 1826 to 1827.

La Paz, Bolivia's seat of government, is the highest capital city in the world, at an elevation of approximately 3,650 m (11,975 ft). Parts of the La Paz conurbation, including the city of El Alto, extend up to 4,200 m (13,780 ft).

Transportation

The rough terrain has historically put the costs of building highways and railroads that cross the Andes out of reach of most neighboring countries, even with modern civil engineering practices. For example, the main crossover of the Andes between Argentina and Chile is still accomplished through the Paso Internacional Los Libertadores. Only recently the ends of some highways that came rather close to one another from the east and the west have been connected.[36] Much of the transportation of passengers is done via aircraft.

However, there is one railroad that connects Chile with Peru via the Andes, and there are others that make the same connection via southern Bolivia. See railroad maps of that region.

There are multiple highways in Bolivia that cross the Andes. Some of these were built during a period of war between Bolivia and Paraguay, in order to transport Bolivian troops and their supplies to the war front in the lowlands of southeastern Bolivia and western Paraguay.

For decades, Chile claimed ownership of land on the eastern side of the Andes. However, these claims were given up in about 1870 during the War of the Pacific between Chile, the allied Bolivia and Peru, in a diplomatic deal to keep Peru out of the war. The Chilean Army and Chilean Navy defeated the combined forces of Bolivia and Peru, and Chile took over Bolivia's only province on the Pacific Coast, some land from Peru that was returned to Peru decades later. Bolivia has been a completely landlocked country ever since. It mostly uses seaports in eastern Argentina and Uruguay for international trade because its diplomatic relations with Chile have been suspended since 1978.

Because of the tortuous terrain in places, villages and towns in the mountains—to which travel via motorized vehicles is of little use—are still located in the high Andes of Chile, Bolivia, Peru, and Ecuador. Locally, the relatives of the camel, the llama, and the alpaca continue to carry out important uses as pack animals, but this use has generally diminished in modern times. Donkeys, mules, and horses are also useful.

Agriculture

The ancient peoples of the Andes such as the Incas have practiced irrigation techniques for over 6,000 years. Because of the mountain slopes, terracing has been a common practice. Terracing, however, was only extensively employed after Incan imperial expansions to fuel their expanding realm. The potato holds a very important role as an internally consumed staple crop. Maize was also an important crop for these people, and was used for the production of chicha, important to Andean native people. Currently, tobacco, cotton and coffee are the main export crops. Coca, despite eradication programmes in some countries, remains an important crop for legal local use in a mildly stimulating herbal tea, and, both controversially and illegally, for the production of cocaine.

Irrigation

Irrigating land in the Peruvian Andes

In unirrigated land, pasture is the most common type of land use. In the rainy season (summer), part of the rangeland is used for cropping (mainly potatoes, barley, broad beans and wheat).

Irrigation is helpful in advancing the sowing data of the summer crops which guarantees an early yield in the period of food shortage. Also, by early sowing, maize can be cultivated higher up in the mountains (up to 3,800 m (12,500 ft)). In addition it makes cropping in the dry season (winter) possible and allows the cultivation of frost resistant vegetable crops like onion and carrot.[37]

Currently, mining in the Andes of Chile and Peru places these countries as the first and third major producers of copper in the world. Peru also contains the 4th largest goldmine in the world: the Yanacocha. The Bolivian Andes produce principally tin although historically silver mining had a huge impact on the economy of 17th century Europe.

^W. van Immerzeel, 1989. Irrigation and erosion/flood control at high altitudes in the Andes. Published in Annual Report 1989, pp. 8–24, International Institute for Land Reclamation and Improvement, Wageningen, The Netherlands. On line: [1]